Project Summary/Abstract Genetics underlie susceptibility to inflammatory bowel disease (IBD) but the rapid rise in incidence, as well as low concordance rates, point to a prevalent role for the environment and possibly the epigenome. Dysregulation of epigenetic enzymes is a recurrent and sentinel event in cancer, making proteins that ?write?, ?erase? and ?read? the epigenome some of the most promising and intently pursued targets in drug discovery today. Despite this, virtually nothing is known about how altered epigenetic enzymes contribute to immunological disorders, including IBD. The long-term goal of the proposed research is to determine how epigenetic alterations influence IBD and accurately decipher the disease-causing mechanisms for better therapeutic strategies. Speckled Protein 140 (SP140) is an epigenetic ?reader? protein with immune-restricted expression. Single nucleotide Polymorphisms (SNPs) within SP140 associate with Crohn's disease (CD) (1, 2) however, the function of SP140 and the consequences of SP140 SNPs have remained unclear. We found CD- associated SP140 SNPs resulted in altered SP140 mRNA splicing and a loss of SP140 protein (4). We also identified SP140 as a key orchestrator of macrophage transcriptional programs essential for cellular identity and function (4). Furthermore, we found that hematopoietic depletion of Sp140 in mice exacerbated colitis and a loss of SP140 due to genetic variation contributed to a subset of CD characterized by suppressed innate immunity (4). The overall objective of the present proposal, which is the next step towards attainment of our long-term goal, is to utilize multiple resources from the IBD Genetics Consortium to precisely define the roles of SP140 in mediating protective innate and adaptive immunity toward commensal microorganisms, and determine how common or rare variants of SP140 impacts these ascribed functions. Guided by compelling preliminary data, our hypotheses will be tested in three specific aims: 1) Elucidate the role of SP140 in protective innate immunity toward commensal microorganisms; 2) Define the role of SP140 in B cell development and function; and 3) Determine the mechanism of SP140 as an epigenetic regulator. Under the first and second aims we will utilize our inducible SP140 depletion system in mice and in parallel examine cells from patients carrying SP140 variants. For aim 3 we will determine the precise mechanism by which SP140 regulates immune cell identity and function. The approach is innovative in the applicant's opinion because the work will be one of the first descriptions of altered epigenetic enzyme expression and function as a driver of immune-mediated disease. The proposed research is significant because SP140 variants are associated with CD, MS and CLL so understanding the function of SP140 will aid understanding of, and stratification of, these diseases. Ultimately, such knowledge has the potential to vertically advance development of novel therapeutics for CD and other immune disorders.